I2C 读取 function 发送确认位后卡住

Question

I'm trying to communicate with a MPU-9250 (Accelerometer and a lot of other stuff) from my PIC16F1789. My functions look like the following:

void i2cWait(){
  while((SSP1STAT & 0x04) || (SSP1CON2 & 0x1F));
}

unsigned char i2cReadCycle(unsigned char regAddr){
    unsigned char val;
    // Start
    i2cWait();
    SEN = 1;

    // Address + Write Bit
    i2cWait();
    SSPBUF = (slvAdd<<1 | (0b1<<0)); // address slave + write
    i2cWait();

    //Register address
    SSP1BUF = regAddr; // address register + read
    i2cWait();

    //Start
    SEN = 1;
    i2cWait();

    // Address + Read Bit
    SSP1BUF = ((slvAdd<<1) | (0b0<<0)); //Address + read (0)
    i2cWait();

    // Daten Auslesen
    RCEN = 1;
    i2cWait();
    val = SSP1BUF;
    i2cWait();
    ACKDT = 1; // set acknowledge Bit (1 = Not Acknowledge, 0 = Acknowledge)
    ACKEN = 1; // send acknowledge Bit

    // Stop
    i2cWait();
    PEN = 1;

    return val;
}

I've worked with the "Single-Byte Read Sequence" on page 35 of the 9250 Datasheet: https://cdn.sparkfun.com/assets/learn_tutorials/5/5/0/MPU9250REV1.0.pdf

And the PIC Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/40001675C.pdf

When debugging, the program gets stuck in the i2cWait() after I send the NACK Bit. It gets stuck because the ACKEN Bit (Bit 4) of the SSPCON2 register (Page 341 of PIC datasheet) doesn't get cleared, so the program gets stuck in the while().

Why doesnt the Bit get cleared by hardware?

Answer 1

It looks like you are using 0b1<<0 for "writing" together with the slave address. However, according to the datasheet of MPU9250REV1.0, it should be 0. Check section 7.4 on page 35.

Although it might be counter-intuitive to set '0' for writes, it makes sense if you think of the "General Call" that ist initiated with the slave address 0b0000000 and the "write" bit 0.

This also means to change the "read" bit in your code to 1.

In the current implementation, mixing up read and write bits, leads to the issue being stuck waiting after setting the NACK.